I have read the forums regarding the 4G LTE issues. I just wanted to add another city to the list...
I have a new S4 Mini (4.2.2. MK2 update) and have checked all the obvious settings. My phone will only connect to 3G (no 4G LTE at all, not even for a few seconds) when I am anywhere in Palm Coast Florida that shows "4G Full Coverage" on the Sprint coverage map.
To be certain that my 4G radio isn't broken I drove up to a different 4G market (St Augustine Florida) and was getting 4G LTE there without doing anything different on the phone. It just picked it up and started using it.
But no 4G LTE in Palm Coast. I am leaning toward it being a tri-band phone issue and that I'll just have to wait for Sprint to fix it on their end. Because I really don't want to take it to a Sprint store and them say "we'll have to hard reset it" (because they don't understand the problem) and then it still not work.
If anybody thinks this is NOT a network issue (especially other 4G LTE users in the Palm Coast area with a new Sprint Spark phone) please reply or private message me. I'd just like to know if this is just me or if it's everybody.
If it matters I ordered my phone directly from Sprint over the Thanksgiving weekend. I activated it and they are assuring me it is not a SIM card issue (which makes some sense otherwise why would it work in a different area?).
I figured out if I am in a local "4G Full Coverage area" (according to Sprint coverage maps) and then enable airplane mode on my phone, and then disable airplane mode, it lights up the 4G LTE icon and locks signal and even works for about 1 to 30 seconds. If I have the speedtest app already loaded I can even start the test and it starts downloading at well over 20Mbps until the moment it switches back to 3G and the test hangs. To be clear: Even in "full coverage" areas in my home city the only way I can get 4G to work at all is to enable airplane mode and disable it which apparently triggers a signal rescan. It's almost like the 3G signal is overpowering the 4G signal and forcing the phone to lock to the inferior network?
Again this is on the new Galaxy S4 Mini triband "Sprint Spark" enabled phone.
Can anyone from Sprint shed any light on this? Is it just going to start working someday? Am I the only person in this city who bought an S4 Mini?
PARTIAL SOLUTION (for now):
Ok this might be really big for those of you who are in a 4G LTE area with a tri-band phone, but who can only get / stay connected by enabling / disabling airplane mode...
I found an app in the google play store: LTE Discovery
If you are within LTE coverage (obviously it won't work if you aren't within an LTE coverage area) and you lose LTE due to (apparent) tri-band issues, this app will automatically toggle your radio off/on, which will then reconnect you to LTE automatically. And if it drops again, it reconnects you again. It runs in the background so you don't have to do anything.
It essentially forces your phone to stay on LTE. You can set it to almost instantly reconnect you to LTE if your phone switches itself back to 3G.
Obviously this is a kludge, but let me tell you it sure beats manually toggling airplane mode over and over!
Tested and working on my Samsung Galaxy S4 Mini. Will continue to provide updates here as warranted.